The use of thermoplastics in thick-film conductor formulations for printing circuits is known. However, the use of thermoplastics in thick-film conductor formulations often results in the spreading of the printed lines upon drying. This is particularly a problem where printed conductor lines intersect at dielectric crossovers. When the temperature of printed conductor lines including thermoplastic polymers is increased at drying, the viscosity of the thermoplastics decrease, resulting in a spreading of the conductor ink used to print the conductor lines. As a result, shorting, or near shorts, may occur when parallel conductor lines are printed at dielectric crossovers. The problem is exacerbated when the conductor line is co-fired with one of the layers of the crossover dielectrics, because of the high steps which occur at these crossover geometries. Thus, heretofore, there has been a need to prevent the spread of thick-film conductor thermoplastic formulations upon firing.
A related problem occurs when inks are printed in through-holes. Although clear after printing, many inks "slump" during drying, blocking the through-hole. To control the problem, the visco-elasticity of the ink is increased. However, this may result in an ink which is too thick for optimal printing of other features.